Drilling tools, such as drilling motors, may be used to provide rotational force to a drill bit when drilling earth formations. Drilling motors used for this purpose may be driven by drilling fluids pumped from surface equipment through a drill string. This type of motor may be referred to as a mud motor. In use, the drilling fluid may be forced through the mud motor, which may extract energy from the flow to provide rotational force to a drill bit located below the mud motor. A mud motor may include a positive displacement motor (PDM) or a turbodrill.
In one scenario, a turbodrill may use turbine stages to provide rotational force to a drill bit. The turbine stages may consist of one or more non-moving stator vanes and a rotor assembly having rotating vanes mechanically linked to a shaft. The turbine stages may be designed such that the vanes of the stator stages direct the flow of drilling fluid into corresponding rotor blades to provide rotation to the shaft, where the shaft ultimately connects to and drives the drill bit. Thus, the high-speed drilling fluid flowing into the rotor vanes may cause the rotor and the drill bit to rotate with respect to a housing.
While providing rotational force to the shaft, the turbine stages may also produce a downhole axial force, or thrust, from the drilling fluid. The downhole thrust, however, may produce a higher weight on bit (WOB) than appropriate for operation of the turbodrill. To mitigate the effects of excess thrust in the turbodrill, thrust bearings may be provided.